No Moon, no life on Earth, suggests theory

http://www.newscientist.com/news/new...d=3Dns99994786



No Moon, no life on Earth, suggests theory


Without the Moon, there would have been no life on Earth.

Four billion years ago, when life began, the Moon orbited much closer to =
us than=20
it does now, causing massive tides to ebb and flow every few hours. These=
tides=20
caused dramatic fluctuations in salinity around coastlines which could ha=
ve=20
driven the evolution of early DNA-like biomolecules.

This hypothesis, which is the work of Richard Lathe, a molecular biologis=
t at=20
Pieta Research in Edinburgh, UK, also suggests that life could not have b=
egun on=20
Mars.

According to one theory for the origin of life, self-replicating molecule=
s such=20
as DNA or RNA emerged when small precursor molecules in the primordial "s=
oup"=20
polymerised into long strands. These strands served as templates for more=
=20
precursor molecules to attach along the templates, creating double-strand=
ed=20
polymers similar to DNA.

But the whole theory fails without some way of breaking apart the double =
strands=20
to keep the process going, says Lathe. It would take some external force =
to=20
dissociate the two strands, he says.


Doubling up

As an analogy, he points to PCR, the technique used to amplify DNA in the=
lab.=20
DNA is cycled between two temperatures in the presence of appropriate enz=
ymes.

At the lower temperature of about 50 =FDC, single DNA strands act as temp=
lates for=20
synthesising complementary strands. At the higher temperature of about 10=
0 =FDC,=20
the double strands break apart, doubling the number of molecules. Lower t=
he=20
temperature, and the synthesis starts again. Using this process, a single=
DNA=20
molecule can be converted into a trillion identical copies in just 40 cyc=
les.

Lathe believes that thanks to the Moon, something similar happened during=
=20
Earth's early years. Most researchers agree that the Moon formed five bil=
lion=20
years ago from debris blasted off Earth in a giant impact.

A billion years later when life is thought to have arisen, the Moon was s=
till=20
much closer to us than it is now. That, plus the Earth's much more rapid =

rotation, led to tidal cycles every two to six hours, with tides extendin=
g=20
several hundred kilometres inland, says Lathe. Coastal areas therefore sa=
w=20
dramatic cyclical changes in salinity, and Lathe believes this led to rep=
eated=20
association and dissociation of double-stranded molecules similar to DNA.=


When the massive tides rolled in, the salt concentration was very low.=20
Double-stranded DNA breaks apart under such conditions because electrical=
ly=20
charged phosphate groups on each strand repel each other.

But when the tides went out, precursor molecules and precipitated salt wo=
uld=20
have been present in high concentrations. This would have encouraged=20
double-stranded molecules to form, since high salt concentrations neutral=
ise=20
DNA's phosphate charges, allowing strands to stick together.


Unrelenting cycles

These unrelenting saline cycles would have amplified molecules such as DN=
A in a=20
process similar to PCR, says Lathe. "The tidal force is absolutely import=
ant,=20
because it provides the energy for association and dissociation [of polym=
ers]."

Many researchers do not believe DNA and RNA were the first replicating=20
molecules. Graham Cairns-Smith of the University of Glasgow, UK, thinks m=
uch=20
simpler "genetic" material formed first, from the crystallisation of clay=
minerals.

But he says Lathe's idea deserves attention. "Whatever the replicating en=
tities=20
were that started the evolutionary process, it would be significant that =
they=20
lived in an environment in which the conditions were changing."

If the theory is right, life could not have evolved on Mars, says Lathe. =
Phobos,=20
the larger of Mars's two Moons, is so small that the tidal forces it gene=
rates=20
are just one per cent of those generated by our Moon. "Even if there was =
water=20
on Mars, life could not have evolved there because these polymers could n=
ot have=20
replicated," he says.

Journal reference: Icarus (vol 168, p 18)

Rich wrote in message ...
http://www.newscientist.com/news/news.jsp?id=ns99994786

....snip...

Many researchers do not believe DNA and RNA were the first replicating
molecules. Graham Cairns-Smith of the University of Glasgow, UK, thinks m
uch
simpler "genetic" material formed first, from the crystallisation of clay
minerals.


I'm glad they included the above; if the other researchers are
correct, Lathe's (and predecessors') tidal-life-genesis hypothesis is
invalid. It also ignores panspermian possibilities (especially if
that Kerala, India 'red-rain' self-replicating protein is real!)


But he says Lathe's idea deserves attention. "Whatever the replicating en
tities
were that started the evolutionary process, it would be significant that
they
lived in an environment in which the conditions were changing."

If the theory is right, life could not have evolved on Mars, says Lathe.
Phobos,
the larger of Mars's two Moons, is so small that the tidal forces it gene
rates
are just one per cent of those generated by our Moon. "Even if there was
water
on Mars, life could not have evolved there because these polymers could n
ot have
replicated," he says.

Journal reference: Icarus (vol 168, p 18)

I won't speak for Mars, but the argument that Earth-life needed the
Moon to get started is an oldie-but-a-goodie. Although the Sun's
tidal effect on Earth is only ~0.46 times that of the Moon (per Isaac
Asimov in the book Extra-terrestrial Civilizations, Crown Publishers,
Inc. c.1979), even without the Moon present, there would still be
(albeit a very minor) tide on Earth, but Earth's rotational speed
would stay roughly the same as it was since formation (i.e. perhaps 10
hours or less for one proto-Earth day?) It would to this day have had
daily minor tidal cycles ~2.4 times higher than today's rate (i.e. 4.8
tides, 2.4 lows, 2.4 highs within 24 hours.) This combined with much
higher wind energy, which would be higher than today's rate because
the more rapidly rotating Earth would impart rotational energy in much
greater amounts to the atmosphere, and oceans, because of the coriolis
force (in conjunction with meridional circulation.) Ocean wind
energies and turbulance would perhaps accentuate the weak solar tidal
influence (such as the moon's tidal influence is enhanced by
hurricanes.) There would still be a land-water coastal interface, and
I don't think that anyone has attempted to guess yet what effect much
greater wind energies and Earth rotational speed would have on tidal
plains and inter-tidal zones (although it perhaps would lead to much
faster coastal erosion to the point of having ginormous tidal plains
and smaller land masses?)

Regards, Jason H.

Big oops,

Jason H. (I) wrote:
Although the Sun's
tidal effect on Earth is only ~0.46 times that of the Moon

I meant to say only ~0.46 that of the Moon.

Sorry, Jason H.